I have some experience in this matter, so allow me to chime in.

Kapalabhati is a breathing technique more useful for bodily purposes than meditation. If you examine your state of mind closely after a vigorous round of Kapalabhati, you will realize that your mind feels 'full' and 'energetic', not 'calm' - that's because kapalabhati is designed to saturate the body with a higher dose of prana. Vigorous breathing does not center the mind - it enlivens it, so to speak.

For pranayamas useful as preparatory to meditation, I would suggest the Bhramari with a focus on the humming sound (Ong, or as wrongly written, Om). It is a good example of nada. Alternatively, per the Buddha, the breath-awareness meditation (centering awareness on the flow of breath) is also excellent.

The true benefit of pranayama for meditation comes from the kumbhaka, the breath retention stage. A higher capacity for kumbhaka, attained after a long practice of various pranayama exercises, allows the meditator to have a longer session of dharana/dhyana.

Many people are misled by some gurus in India about Pranayama. Its time we set the record straight.